Web welding system

ABSTRACT

An object of the present invention is to provide a welding system wherein the positional accuracy of welding and the quality of welding are improved. The present welding system includes an ultrasonic welder for welding a plurality of webs W together while carrying the webs W. The ultrasonic welder includes: an anvil roller  10  including a pair of anvils  11, 12 ; a first ultrasonic horn  21  and a second ultrasonic horn  22  that apply vibration energy to the webs W in cooperation with the pair of anvils  11, 12 . The pair of anvils  11, 12  are provided symmetrically with each other with respect to an axis line O of the anvils roller  10 . The first and second ultrasonic horns  21, 22  apply the vibration energy to the webs W simultaneously while each of the anvils  11, 12  faces the first or second ultrasonic horn  21, 22.

TECHNICAL FIELD

The present invention relates to a welding system for welding aplurality of webs, which is sometimes referred to as “sealing”.

BACKGROUND ART

Hitherto, a welding system wherein a plurality of ultrasonic horns areprovided around one anvil roller is known (for example, the followingfirst patent document).

The first patent document: Japanese Laid-Open Patent Publication No.2004-330622 (abstract)

DISCLOSURE OF THE INVENTION

However, in such a conventional welding system, since a plurality ofultrasonic horns are provided around one anvil roller, the anvil rolleris subject to large loads caused by ultrasonic vibration energy. Thus,the durability of the anvil roller may be impaired. Further, when theultrasonic horns apply ultrasonic vibration simultaneously to the websto weld the webs, the vibration causes positional displacement of theanvil roller. Accordingly, positional accuracy of welding may bedecreased or quality of welding may be decreased.

An object of the present invention is to provide a new welding systemwherein the positional accuracy of welding and the quality of weldingare improved and the durability of the anvil roller is enhanced.

In order to achieve the object, a welding system of the presentinvention includes an ultrasonic welder for welding a plurality of webstogether while carrying the webs.

The ultrasonic welder comprises an anvil roller including a pair ofanvils and a first ultrasonic horn (vibrating body) and a secondultrasonic horn (vibrating body) that apply vibration energy to the websin cooperation with the pair of anvils. The pair of anvils are providedsymmetrically with each other with respect to an axis line of the anvilsroller.

The first and second ultrasonic horns are arranged so that one anvil ofthe pair can face the first ultrasonic horn at the same time as theother anvil of the pair faces the second ultrasonic horn.

This system includes carrying means for carrying the webs so that thewebs pass a first gap between the anvil roller and the first ultrasonichorn and then pass a second gap between the anvil roller and the secondultrasonic horn.

The first and second ultrasonic horns apply the vibration energy to thewebs simultaneously while each of the anvils faces the first or secondultrasonic horn.

In this system, the welding of the webs is performed simultaneously attwo locations. At this time, two opposite forces from the ultrasonichorns approximately toward the center of the anvil roller are appliedsimultaneously to the anvil roller via the webs.

Since the anvil roller receives simultaneously the two forces that arein opposite directions to each other, shock loads applied to the anvilroller due to the ultrasonic vibration energy is decreased, which makesthe anvil roller less readily displace even when the ultrasonic hornsapplies the vibration energy to the anvil roller. Accordingly, thepositional accuracy of the welding is improved.

According to a preferred aspect of the present invention, the weldingsystem further comprises a velocity-changing device for increasing anddecreasing a moving velocity of the webs.

By the velocity-changing device, the moving velocity of the webs at thefirst and second gaps when the first and second ultrasonic horns applythe vibration energy to the webs is set smaller than that at a positionwhere the webs enter into the velocity changing device and/or that at aposition where the webs exit from the velocity-changing device.

In this aspect, since the webs have longer time to receive the vibrationenergy, the quantity of the received vibration energy per unit area ofthe webs is increased. Accordingly, the reliability of the welding canbe enhanced.

Furthermore, since the two ultrasonic horns are actuated simultaneously,the number of times the velocity-changing device changes the movingvelocity of the webs can be decreased, and so, the number of times aprime mover (servo motor) of the velocity-changing device is subject toloads caused at the time of changing the moving velocity and the numberof times dancer rollers of the velocity-changing device are moved can behalved. Accordingly, the durability of the device is enhanced.

In this aspect, the velocity-changing device may comprises: a firstdancer roller that receives the webs flowing from an upstream side andreleases the webs toward the first gap; a second dancer roller thatreceives the webs released from the second gap and releases the webstoward a downstream side; and moving means for moving the first andsecond dancer rollers. In this structure, the moving means may move thefirst roller and the second roller in generally opposite directions witheach other so that the moving velocity of the webs is increased anddecreased.

According to another preferred aspect of the present invention, thewelding system further comprises a velocity-changing device forincreasing and decreasing a moving velocity of the webs. Thevelocity-changing device comprises: a first dancer roller that receivesthe webs flowing from an upstream side and releases the webs toward thefirst gap; a second dancer roller that receives the webs released fromthe second gap and releases the webs toward a downstream side; movingmeans for moving the first and second dancer rollers; and a firstdriving means for rotatably driving the first and second dancer rollers.

In this aspect, a distance between the first and second dancer rollersmay be substantially equal to or smaller than a diameter of the anvilroller.

If the distance between the two dancer rollers is large, the entiresystem including the velocity-changing device would be large in size. Onthe contrary, if, as mentioned above, the distance between the dancerrollers is approximately the same as or smaller than the diameter, theentire system becomes small in size.

It is preferred that the web welding system of this aspect furthercomprises a timing belt trained around a plurality of rollers includingthe first and second dancer rollers and a drive roller, for rotating theplurality of rollers in synchronism.

In this case, since the distance between the dancer rollers is small,the timing belt can be shortened. Accordingly, a commercially availabletiming belt becomes adoptable.

In addition, the web welding system may further comprise: a drive rollerwhich the timing belt is trained about, the drive roller rotatablydriven by the first driving means; a second driving means for rotatablydriving the adjustment roller; and a control device. In this case, thecontrol device controls the moving means, the first driving means andthe second driving means so that both of a circumferential velocity ofthe adjustment roller and a circumferential velocity of the drive rollerare equal to the moving velocity of the webs between the first andsecond dancer rollers.

According to another preferred aspect of the present invention, wheneach anvil of the pair faces the first ultrasonic horn or the secondultrasonic horn, the first and second ultrasonic horns are controlled toapply the vibration energy to the webs so that ultrasonic welding of thewebs is performed. On the other hand, when the ultrasonic welding of thewebs is not performed, the first and second ultrasonic horns arecontrolled not to apply the vibration energy to the webs.

In this aspect, since the horns need not be actuated continuously,electric power cost can be reduced. Furthermore, since the vibrationenergy is not applied to a portion of the webs which does not requirethe welding, the portion of the webs is unlikely to be creased.

According to another preferred aspect of the invention, the carryingmeans comprises: a adjustment roller that is rotatably supported;supporting means for rotatably supporting the adjustment rollerselectively at a first position or a second position which is differentfrom the first position. The webs flowing out of the first gap flowalong an outer circumferential surface of the adjustment roller, andthen are carried into the second gap.

When a semi-finished product including the webs is to be processed intoa worn article of a first size, the adjustment roller is supported atthe first position by the supporting means. On the other hand, when thesemi-finished product including the webs is to be processed into a wornarticle of a second size that is different from the first size, theadjustment roller is supported at the second position by the supportingmeans.

The first and second ultrasonic horns weld a portion of the webs that isto be an end portion of an individual worn article, respectively, thelength of the webs between the first gap and the second gap correspondsto the length of the product, i.e., the worn article, or a multiplethereof. Accordingly, the length of the produced worn article can bechanged by means of changing the position where the adjustment roller issupported. That is, since the intervals of welded portions of the webcan be adjusted by means of changing the position of the adjustmentroller, one web welding system can produce worn articles of varioussizes.

In this aspect, an angular velocity of the anvil roller may becontrolled so that, according to the size of the worn article to beproduced, one anvil of the pair can face the first ultrasonic horn atthe first gap at the same time as the other anvil of the pair faces thesecond ultrasonic horn at the second position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view showing a welding system of the firstembodiment.

FIG. 2( a) is a schematic side view of a velocity-changing device andFIG. 2( b) is a schematic side view showing another example of an anvilroller.

FIG. 3 is a schematic configuration diagram showing an control system.

FIGS. 4( a) to 4(c) are a schematic elevation views each showing anexample of worn articles before separating each other.

FIG. 5 is a schematic side view showing a welding system of anotherembodiment.

FIG. 6 is a schematic side view showing a welding system of yet anotherembodiment.

DESCRIPTION OF THE REFERENCE NUMERALS

1: First gap

2: Second gap

3: Carrying means

4: Velocity-changing device

5: Control device

10: Anvil roller

11, 12: Anvil

21: First ultrasonic horn

22: Second ultrasonic horn

31: Supporting means

32: Second driving means

40: Moving means

41: First driving means

P1: First position

P2: Second position

R1: First dancer roller

R2: Second dancer roller

R3: Adjustment roller

R4: Drive roller

TB: Timing belt

W: Web

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be understood more clearly from the followingdescription of preferred embodiments taken in conjunction with theaccompanying drawings. However, it will be appreciated that theembodiments and the drawings are given for the purpose of mereillustration and explanation and that the scope of the present inventionis to be defined by the appended claims. In the accompanying drawings,the same reference numerals denote the same or corresponding elementsthroughout several figures.

Embodiments of the present invention will now be described withreference to the drawings.

In the following description, an important part of a web welding systemof the present invention will first be described in the firstembodiment, and a velocity-changing device that is provided in the webwelding system will then be described.

FIGS. 1 to 3 show the first embodiment.

The present system includes an ultrasonic welding device (ultrasonicwelder) for welding together a plurality of webs W, which are stacked oneach other, while carrying the webs W. The ultrasonic welder includes:an anvil roller 10 including a pair of anvils 11, 12; a first ultrasonichorn 21 and a second ultrasonic horn 22 that apply vibration energy tothe webs W in cooperation with the pair of anvils 11, 12; a pair ofultrasonic devices 20, 20 that generates ultrasonic vibration in theultrasonic horns 21, 22, respectively.

High frequency mechanical vibrations is transmitted to the ultrasonichorns 21, 22 so that the webs W passing between the ultrasonic horn 21,22 and the anvil 11, 12 are welded (fusion-bonded) with each other dueto frictional heat.

As the ultrasonic horns 21, 22, for example, the ultrasonic horndisclosed in Japanese National Phase PCT Laid-Open Publication No.10-513128 may be used. The surfaces of the ultrasonic horns 21, 22 maybe embossed with a seal pattern having many protrusions. Alternatively,the surfaces of the anvils 11, 12 may be embossed with a seal patterninstead of embossing the surfaces of the ultrasonic horns 21, 22.

The webs W are formed by stacking a plurality of thermoplastic resinwebs that have to be welded with each other. Welded areas Sa1, Sa2, Sa3of the webs W, which areas are sealed by the ultrasonic devices 20, 20,constitute end portions of individual disposable pants (an example ofthe worn article), as shown in FIGS. 4( a) to 4(c). The pitch (interval)of the welded areas Sa1, Sa2, Sa3 is set to a predetermined length Spm,Spl, in advance.

The pair of anvils 11, 12 are provided symmetrically with each otherwith respect to an axis line of the anvils roller 10, i.e., a line thatextends along the center O of rotation of the anvils 11, 12. That is,the pair of anvils 11, 12 are provided on the anvil roller 10 at anangular pitch of 180 degrees.

The first and second ultrasonic horns 21, 22 are positionedsymmetrically with each other with respect to the center of rotation ofthe anvils 11, 12. That is, the pair of ultrasonic horns 21, 22 arearranged so that one of the pair of anvils 11, 12 can the firstultrasonic horn 21 simultaneously with the other of the pair of anvils11, 12 facing the second ultrasonic horn 22.

The pair of ultrasonic horns 21, 22 apply the vibration energy onto thewebs W simultaneously in a state where one of the pair of anvils 11, 12faces the first ultrasonic horn 21 and where the other of anvils 11, 12faces the first ultrasonic horn 22. Thus, the welding of the webs W isperformed at two locations simultaneously. At the time of this welding,the anvil roller 10 receives two forces of opposite directions towardthe center 0 of the anvil roller 10, simultaneously, via the webs W,from the ultrasonic horns 21, 22, respectively. Since the anvil roller10 receives simultaneously the two forces that are in oppositedirections to each other, the anvil roller 10 comes to less readilydisplace even when the ultrasonic horns 21, 22 applies large vibrationenergy to the anvil roller 10.

As shown in FIG. 2( b), another pair of anvils 13, 14, or another pluralpairs of anvils, may be provided on the anvil roller 10, in addition tothe pair of anvils 11, 12.

The present system includes a transport apparatus 3 (carrying means forcarrying the webs W). This transport apparatus 3 carries the webs W sothat the webs W pass a first gap 1 between the anvil roller 10 and thefirst ultrasonic horn 21 and then pass a second gap 2 between the anvilroller 10 and the second ultrasonic horn 22. The transport apparatusincludes an adjustment roller R3, a velocity-changing device 4, whichwill be described in detail later, and so on. The webs W having passedthe first gap 1 flow along an outer circumferential surface of theadjustment roller R3, and then is carried into the second gap. Note thatthe ultrasonic device 20, 20, the transport apparatus 3 and the like,are arranged so that the upstream side and the downstream side thereofare in mirror symmetry with each other.

The adjustment roller R3 is rotatably supported by supporting means 31.The supporting means 31 rotatably support the adjustment roller R3selectively at a first position P1 or a second position P2, whichpositions are different from each other.

In a case where a worn article of the first size (for example, mediumsize) shown in FIG. 4( a) is to be produced, the adjustment roller R3 issupported at the first position P1 shown by solid line in FIG. 1, by thesupporting means 31. On the other hand, in a case where a worn articleof the second size (for example, large size) shown in FIG. 4( c) is tobe produced, the adjustment roller R3 is supported at the secondposition P2 shown by one-dot chain line in FIG. 1, by the supportingmeans 31.

The welded areas Sa1, Sa2, Sa3 of the worn article N shown in FIGS. 4(a) to 4(c) are formed by welding a portion of the webs W at the firstgap 1 and the second gap 2 while the webs W go through the gaps 1, 2.The welding at the first gap 1 and the welding at the second gap 2 areperformed simultaneously. Accordingly, the length of a portion of thewebs W between the first gap 1 and the second gap 2 need to be set to anintegral multiple of the pitch (product length) Spm, Spl of the wornarticle N. By supporting the adjustment roller R3 shown in FIG. 1selectively at the first position P1 or the second position P2 with theweb length kept as above mentioned, worn articles of more than twodifferent sizes can be produced in one system.

The structure of the supporting means is not limited to any specificstructure, but the supporting means 31 may have, for example, astructure wherein the center O3 of rotation of the adjustment roller R3is fixed to a pivot arm which is lockable at two different angularpositions. Alternatively, the supporting means 31 may have a structurewherein a bearing supporting the adjustment roller R3 can be fixedselectively among two or more different positions. The supporting means31 may have a structure wherein worn articles of three or more sizes canbe produced.

The velocity-changing device 4 includes the first dancer roller R1, thesecond dancer roller R2, moving means 40 (FIG. 2( a)) and the firstdriving means 41. The first dancer roller R1 (FIG. 1) receives the websW flowing from the upstream side and releases the webs W toward thefirst gap 1. The second dancer roller R2 receives the webs W flowingfrom the second gap 2 and releases the webs W toward the downstreamside.

The moving means 40 (FIG. 2) reciprocates (swings) the first and seconddancer rollers R1, R2, as shown by two-dot line and solid line inFIG. 1. The first driving means 41 rotates the first and second dancerrollers R1, R2 at the same rotational velocity (circumferentialvelocity).

The first guide roller G1 is rotatably provided on the upstream side ofthe first dancer roller R1. The second guide roller G2 is rotatablyprovided on the downstream side of the second dancer roller R2. Thefirst guide roller G1 guides the webs W flowing toward the first dancerroller R1. The second guide roller G2 guides the webs W flowing out ofthe second dancer roller R2. Between and above the dancer rollers R1,R2, the first drive roller R4 is located. As shown in FIG. 2( a), atiming belt TB is trained around the above mentioned five rollers R1,R2, G1, G2, R4 and a tension roller Rt, etc. Accordingly, this timingbelt TB enables the five rollers R1, R2, G1, G2, R4 to rotate insynchronism when the drive roller R4 is rotatably driven.

The velocity-changing device 4 alternates between transport of the websW at a high moving velocity and transport of the webs W at a low movingvelocity, repeatedly. In the transport of the webs W at the high movingvelocity, the moving velocity of the webs W between the dancer rollersR1, R2 is larger than the velocity V of the web W flowing into the firstdancer roller R1. On the other hand, in the transport of the webs W atthe low moving velocity, the moving velocity of the webs W between thedancer rollers R1, R2 is smaller than the velocity V.

That is, in the transport at the high moving velocity, the webs W istransported at the high moving velocity between the dancer rollers R1,R2, by moving both of the dancer rollers R1, R2 so that, as shown bysolid line arrow D1 in FIG. 1, the first dancer roller R1 gets close tothe anvil roller 10 and, at the same time, the second dancer roller R2gets away from the anvil roller 10. On the other hand, in the transportat the low moving velocity, the webs W is transported at the low movingvelocity between the dancer rollers R1, R2, by moving both of the dancerrollers R1, R2 so that, as shown by broken line arrow D2 in FIG. 1, thefirst dancer roller R1 gets away from the anvil roller 10 and, at thesame time, the second dancer roller R2 gets close to the anvil roller10.

When the first and second anvils 11, 12 faces a portion of the anvilroller 10 other than the first and second ultrasonic horns 21, 22, themoving velocity of the webs W between the first and second dancerrollers R1, R2 is controlled to be larger than the moving velocity ofthe webs W flowing into the first dancer roller R1.

On the other hand, when the anvils 11, 12 faces the first and secondultrasonic horns 21, 22, respectively, the moving velocity of the webs Wbetween the first and second dancer rollers R1, R2 is controlled to besmaller than the moving velocity V of the webs W flowing into the firstdancer roller R1 and at this time the ultrasonic welding of the webs Wis performed.

Thus, when the horns 21, 22 apply the vibration energy onto the webs W,the moving velocity of the webs W passing between the horns 21, 22 andthe anvils 11, 12 is set low. In consequence, the webs W can have moretime to receive the vibration energy and so the quantity of the receivedvibration energy per unit area of the webs is increased. Accordingly,the reliability of the welding can be enhanced.

Furthermore, since the pair of anvils 11, 12 and the pair of horns 21,22 are provided in this system, the number of times the servo motorchanges its rotational velocity is halved as compared to a case whereonly one anvil and one horn are provided. Accordingly, the load on eachservo motor periodically changing its rotational velocity can bereduced. In addition, the number of times the dancer rollers R1, R2 areswung per one product can be halved as compared to a case where only oneanvil and one horn are provided. Accordingly, the burden on the deviceor apparatus is reduced, thereby lengthening its useful life.

Since the first driving means 41 of the velocity-changing device 4 ofFIG. 2( a) makes the pair of dancer rollers R1, R2 rotate at the samerotational velocity and at a circumferential velocity which is equal tothe moving velocity of the webs W, the tension of the webs W between thepair of dancer rollers R1, R2 remains unchanged. In addition, if the twodancer rollers R1, R2 moves at the same moving velocity, the length ofthe webs W between the two dancer rollers R1, R2 can be kept constant.Thus, the webs W are unlikely to expand or contract.

Now, an arrangement of the dancer rollers R1, R2 will be described.

As shown by solid line in FIG. 1, when the dancer rollers R1, R2 arepositioned at the center of the movement, the distance between the firstdancer roller R1 and the anvil roller 10 is substantially equal to thedistance between the second dancer roller R2 and the anvil roller 10.The dancer rollers R1, R2 are arranged in such a way that the distancebetween a releasing position of the first dancer roller R1 where thewebs W are released from the first dancer roller R1 and a receivingposition of the second dancer roller R2 where the second roller R2receives the webs W is set substantially equal to or smaller than thediameter of the anvil roller 10, when the dancer rollers R1, R2 arepositioned at the center of the movement. As a result, compact structureof the velocity-changing device 4 can be realized.

Now, an example of the moving means 40 will be described with referenceto FIG. 2( a).

In this moving means 40, a belt 43 for swinging the dancer rollers R1,R2 is trained around, for example, five pulleys 42. The first and seconddancer rollers R1, R2 are rotatably attached to the belt 43 by the firstand second attachments 44, 45, respectively. This moving means 40includes two groups of the five pulleys 42 and the belt 43, and thegroups are placed beside the dancer rollers R1, R2 on opposite sides ofthe web flowing direction.

One of the five pulleys 42 is a drive pulley. This drive pulley isrotated in forward and reverse directions by a servo motor (not shown).The rotation of the servo motor in the forward direction makes the belt43 move in the first direction D1 of solid line arrow, and, as a result,the first and second dancer rollers R1, R2 move in the first directionD1. On the other hand, The rotation of the servo motor in the reversedirection makes the belt 43 move in the second direction D2 of brokenline arrow, and, as a result, the first and second dancer rollers R1, R2move in the second direction D2.

Both dancer rollers R1, R2 repeated reciprocating motion (swingingmotion) in the directions D1, D2, thereby that the transport of the websW at the high moving velocity and the transport of the webs W at the lowmoving velocity are performed alternately and repeatedly, as abovementioned.

Now, the control of the present system will be described.

As shown in FIG. 3, in this system, the control device 5 controls theultrasonic devices 20 of the ultrasonic welder and the servo motors ofthe anvil roller 10, the first driving means 41, the second drivingmeans 32 and the moving means 40. The second driving means 32 rotatablydrives the adjustment roller R2 (FIG. 1) via the servo motor.

The control device 5 controls the ultrasonic device 20 and the servomotor of the anvil roller 10 so as to build the following relationshipbetween the timing of actuating the ultrasonic device 20 and thepositions of the anvils 11, 12 of the anvil roller 10.

The angular velocity of the anvil roller 10 is controlled so that,according to the size (medium size or large size) of the worn article Nshown in FIG. 4( a) and FIG. 4( c), i.e., according to the pitch of thewelded areas Sa1, Sa2, Sa3, one of the pair of anvils 11, 12 can facethe first ultrasonic horn 21 at the first gap 1 (FIG. 1) at the sametime as the other of the pair of anvils 11, 12 faces the secondultrasonic horn 22 at the second gap 2.

The ultrasonic device 20 is controlled so that the first and secondultrasonic horns 21, 22 apply the vibration energy onto the webs W wheneach of the pair of anvils 11, 12 faces the first ultrasonic horn 21 orthe second ultrasonic horn 22, thereby to perform the welding of thewebs W. On the other hand, during the time the ultrasonic welding of thewebs W is not performed, the ultrasonic device 20 is controlled so thatthe first and second ultrasonic horns 21, 22 do not apply the vibrationenergy to the webs W.

The first drive roller R4 is in contact with the webs W being carriedfrom the first dancer roller R1 toward the first gap 1 and in contactwith the webs W being carried from the second gap 2 toward the seconddancer roller R2. Since the timing belt TB (FIG. 2( a)) is trained aboutthe first dancer roller R1, the second dancer roller R2 and the firstdrive roller R4, the rotational velocities of the first drive roller R4and the dancer rollers R1, R2 are changed in synchronism. Accordingly,by controlling the change of the circumferential velocity of the firstdrive motor R4, the circumferential velocity of the first dancer rollerR1 at the releasing point and the circumferential velocity of the seconddancer roller R2 at the receiving point are changed in synchronismaccording to a predetermined velocity curve.

Furthermore, the circumferential velocity of the first drive roller R4and the circumferential velocity of the adjustment roller R3 are changedin synchronism so that both circumferential velocities are kept thesame. The circumferential velocity of the anvil roller 10 and thecircumferential velocity of the first drive roller R4 are periodicallychanged so that both circumferential velocities are the same when theultrasonic welding of the webs W is performed. Thus, the moving means40, the first and second driving means 41, 32 and the anvil roller 10(FIG. 3) are controlled, according to the movement of the dancer rollersR1, R2, so that the circumferential velocity of the first drive rollerR4 and the circumferential velocity of the adjustment roller R3 are keptequal to each other and that the circumferential velocity of the anvilroller 10 and the moving velocity of the webs W between the first andsecond dancer rollers R1, R2 are equal to each other when the ultrasonicwelding of the webs W is performed.

Now, the operation of the present system will be described.

As shown in FIG. 1, the webs W flow from the first guide roller G1 tothe first dancer roller R1 at a generally constant velocity V and thenflow along the outer circumferential surface of the first dancer rollerR1. The webs W having exited from the first dancer roller R1 pass thefirst and second gaps 1, 2 and then flow along the outer circumferentialsurface of the second dancer roller R2. Subsequently, the webs W arecarried toward the second guide roller G2 at a generally constantvelocity V.

When the ultrasonic welding is performed, the first dancer roller R1moves in the direction of arrow D2 so that the length of the webs Wbetween the first dancer roller R1 and the first gap 1 increases, and,at the same time, the second dancer roller R2 moves in the direction ofarrow D2 so that the length of the webs W between the first dancerroller R2 and the second gap 2 decreases. By such a movement of rollersR1, R2, the moving velocity of the webs W becomes smaller than thevelocity V of the webs W entering into the first dancer roller R1.

When the webs W is carried at the low velocity, the anvils 11, 12 of theanvil roller 10 face the ultrasonic horns 21, 22. At this time, theultrasonic device 20 is actuated, and, as a result, the adjacent weldedareas Sa3, Sa3 (FIG. 4( a)) of the webs W are welded (sealed)simultaneously.

When the ultrasonic welding is not performed, the first dancer roller R1moves in the direction of arrow D1 so that the length of the webs Wbetween the first dancer roller R1 and the first gap 1 decreases, and,at the same time, the second dancer roller R2 moves in the direction ofarrow D1 so that the length of the webs W between the first dancerroller R2 and the second gap 2 increases. By such a movement of rollersR1, R2, the moving velocity of the webs W becomes larger than thevelocity V of the webs W entering into the first dancer roller R1.

Regarding the ultrasonic welding, one welded area Sa3 may be welded byboth ultrasonic horns 21, 22, as shown in FIG. 4( a). That is, the firstultrasonic horn 21 apply the vibration energy to a portion of the webs W(welded portion Sa3 in FIG. 4( a)) when either of the pair of anvils 11,12 faces the first ultrasonic horn 21, and then, the second ultrasonichorn 22 apply the vibration energy once again to the portion of the websW (the welded area Sa3), to which the first ultrasonic horn 21 hasapplied the vibration energy, when either of the pair of anvils 11, 12faces the second ultrasonic horn 22. The welded area Sa3 becomes an endportion of the product such as a worn article.

In this case, the moving velocity of the webs W and the angular velocityof the anvil roller 10 are controlled so that the welded area Sa3, whichhas been welded by the first ultrasonic horn 21 at the first gap 1, issubsequently welded by the second ultrasonic horn 22.

In such a welding, since the vibration energy is applied twice to oneportion of the webs W, the reliability of the welding can be enhanced.

On the other hand, as shown in FIG. 4( b), each welded area Sa1, Sa2 maybe welded only by either of the ultrasonic horns 21, 22. That is, wheneither of the pair of anvils 11, 12 faces the first ultrasonic horn 21,the first ultrasonic horn 21 applies the vibration energy to a portion(welded area Sa1 in FIG. 4( b)) of the webs W, and the vibration energyby the second ultrasonic horn 22 is not to be applied to the portion(the welded area) of the webs W to which the first ultrasonic horn 21has applied the vibration energy. When either of the pair of anvils 11,12 faces the second ultrasonic horn 22, the second ultrasonic horn 22applies the vibration energy to another portion (welded area Sa2 in FIG.4( b)) of the webs W where the vibration energy is not applied by thefirst ultrasonic horn 21.

In this case, as shown in FIG. 4( b), the welded area Sa1 welded by thefirst ultrasonic horn 21 and the welded area Sa2 welded by the secondultrasonic horn 22 emerge alternately on the webs W. The pitch betweenthe welded areas Sa1, Sa2 is the length Spm, and therefore, the pitch ofthe welded areas Sa1, Sa1 welded by the first ultrasonic horn 21 and thepitch of the welded areas Sa2, Sa2 welded by the second ultrasonic horn22 are the double of the length Spm, respectively. These welded areasSa1, Sa2 become end portions of the product such as a worn article. Inthis case, the moving velocity of the webs W and the angular velocity ofthe anvil roller 10 are controlled so that, after welded areas Sa1, Sa2are welded at the first and second gap 1, 2, respectively, the webs Ware carried by the double of Spm, and then, other welded areas Sa1, Sa2are welded.

In the case of such a welding, positional misalignment of the welding,which misalignment may occur in the case the vibration energy is appliedtwice to each welded area Sa1, Sa2, is unlikely to occur. Accordingly,in this case, beautiful worn articles can be produced and the percentageof rejects in the production of worn articles decreases, thereby toimprove the production efficiency. In addition, since the ultrasonicwelding is performed only once per one welded area, the number of timesthe dancer rollers the dancer rollers are swung can be reduced, therebyto lengthen the useful life of machine.

FIG. 5 shows the second embodiment.

As shown in FIG. 5, the first drive roller R4 which is in contact withthe webs W need not necessarily be provided.

FIG. 6 shows the third embodiment.

As shown in FIG. 6, guides (guide members) T1, T2, T3 for guiding theflow of the webs W may be provided around the three rollers R1, R2, R3,respectively. Similarly, guides T8, T9 for guiding the flow of the websW may be provided around the first and second guide roller G1, G2. Inaddition, guides T4, T5 for guiding the flow of the webs W flowing intothe first drive roller R4 and guides T6, T7 for guiding the flow of thewebs W flowing out of the first drive roller R4 may be provided. Theseguides T1 to T9 are useful for carrying the webs W smoothly, especiallyin a case where the weight of the webs W is unbalanced, for example, thewebs W is composed of a stack of a plurality of webs including absorbentbodies.

While preferred embodiments of the present invention have been describedabove with reference to the drawings, obvious variations andmodifications will readily occur to those skilled in the art uponreading the present specification.

For example, the adjustment roller and the velocity-changing device neednot necessarily be provided.

Fixed roller may be provided instead of the adjustment roller.

The adjustment roller may be supported at the first or second positionvia means for fine adjusting the position of its shaft center.

In a case where the velocity-changing device is provided, a method forchanging the velocity is not limited to the above embodiments.

Other belts or chains may be used instead of the timing belt.

The dancer roller may move right and left instead of moving up and down.

Thus, such variations and modifications shall fall within the scope ofthe present invention as defined by the appended claims.

INDUSTRIAL APPLICABILITY

The welding system of the present invention is applicable to theproduction facility for producing disposable worn articles such asdisposable pants, disposable diapers and sanitary products and alsoapplicable to the production facility for producing medical wounddressings.

1. A welding system with an ultrasonic welder for welding a plurality ofwebs together while carrying the webs, wherein the ultrasonic weldercomprises: an anvil roller including a pair of anvils; a firstultrasonic horn and a second ultrasonic horn that apply vibration energyto the webs in cooperation with the pair of anvils; and carrying meansfor carrying the webs so that the webs pass a first gap between theanvil roller and the first ultrasonic horn and then pass a second gapbetween the anvil roller and the second ultrasonic horn, the first andsecond ultrasonic horns are arranged so that one anvil of the pair canface the first ultrasonic horn at the same time as the other anvil ofthe pair faces the second ultrasonic horn, and the first and secondultrasonic horns apply the vibration energy to the webs simultaneouslywhile each of the anvils faces the first or second ultrasonic horn,wherein the pair of anvils are provided symmetrically with each otherwith respect to an axis line of the anvil roller.
 2. A welding systemaccording to claim 1, comprising a velocity-changing device forincreasing and decreasing a moving velocity of the webs, wherein by thevelocity-changing device, the moving velocity of the webs at the firstand second gaps when the first and second ultrasonic horns apply thevibration energy to the webs is set smaller than that at a positionwhere the webs enter into the velocity changing device and/or that at aposition where the webs exit from the velocity-changing device.
 3. Awelding system according to claim 2, wherein the velocity-changingdevice comprises: a first dancer roller that receives the webs flowingfrom an upstream side and releases the webs toward the first gap; asecond dancer roller that receives the webs flowing from the second gapand releases the webs toward a downstream side; and moving means formoving the first and second dancer rollers, wherein the moving means canmove the first roller and the second roller in generally oppositedirections with each other so that the moving velocity of the webs isincreased and decreased.
 4. A welding system according to claim 2,wherein the velocity-changing device comprises: a first dancer rollerthat receives the webs flowing from an upstream side and releases thewebs toward the first gap; a second dancer roller that receives the websreleased from the second gap and releases the webs toward a downstreamside; moving means for moving the first and second dancer rollers; and afirst driving means for rotatably driving the first and second dancerrollers.
 5. A welding system according to claim 4, wherein a distancebetween the first and second dancer rollers is substantially equal to orsmaller than a diameter of the anvil roller.
 6. A welding systemaccording to claim 4, further comprising a timing belt trained around aplurality of rollers including the first and second dancer rollers and adrive roller, for rotating the plurality of rollers in synchronism.
 7. Awelding system according to claim 6, further comprising: a drive rollerwhich the timing belt is trained about, the drive roller rotatablydriven by the first driving means; a second driving means for rotatablydriving the adjustment roller; and a control device that controls themoving means, the first driving means and the second driving means sothat both of a circumferential velocity of the adjustment roller and acircumferential velocity of the drive roller are equal to the movingvelocity of the webs between the first and second dancer rollers.
 8. Awelding system according to claim 1, wherein when each anvil of the pairfaces the first ultrasonic horn or the second ultrasonic horn, the firstand second ultrasonic horns are controlled to apply the vibration energyto the webs so that ultrasonic welding of the webs is performed, andwhen the ultrasonic welding of the webs is not performed, the first andsecond ultrasonic horns are controlled not to apply the vibration energyto the webs.
 9. A welding system according to claim 1, wherein thecarrying means comprises: a adjustment roller that is rotatablysupported; supporting means for rotatably supporting the adjustmentroller selectively at a first position or a second position that isdifferent from the first position, and the webs having passed the firstgap flow along an outer circumferential surface of the adjustmentroller, and then are carried into the second gap, wherein when asemi-finished product including the webs is to be processed into a wornarticle of a first size, the adjustment roller is supported at the firstposition by the supporting means, and when the semi-finished productincluding the webs is to be processed into a worn article of a secondsize that is different from the first size, the adjustment roller issupported at the second position by the supporting means.
 10. A weldingsystem according to claim 9, wherein an angular velocity of the anvilroller can be controlled so that, according to the size of the wornarticle to be produced, one anvil of the pair can face the firstultrasonic horn at the first gap at the same time as the other anvil ofthe pair faces the second ultrasonic horn at the second position.
 11. Awelding system according to claim 1, wherein when either anvil of thepair faces the first ultrasonic horn, the first ultrasonic horn appliesthe vibration energy to a portion of the webs, and when either anvil ofthe pair faces the second ultrasonic horn, the second ultrasonic hornapplies the vibration energy once again to the portion of the webs wherethe vibration energy has been applied by the first ultrasonic horn. 12.A welding system according to claim 1, wherein when either anvil of thepair faces the first ultrasonic horn, the first ultrasonic horn appliesthe vibration energy to a portion of the webs, to which portion thevibration energy by the second ultrasonic horn is not to be applied, andwhen either anvil of the pair faces the second ultrasonic horn, thesecond ultrasonic horn applies the vibration energy to another portionof the webs where the vibration energy by the first ultrasonic horn isnot applied.